Congenital heart disease (CHD) affects up to 1% of live births, but its genetic basis is still not well understood. Human studies to unravel the genetic causes of CHD is challenging given genetic diversity of the human population. Genetic analysis in mice is advantageous given the mouse genome is completely sequenced, and inbred mice provide animals that are genetically identical. Knockout mouse studies have identified many genes that can cause CHD. However, ftjnctional redundancies may mask gene function or early embryonic lethality may preclude assessment of CHD. We propose a complementary approach with forward genetic screening with ethylnitrosourea mutagenesis to recover mutations causing CHD. We previously showed noninvasive mouse fetal echocardiography is highly effective for high throughput Cardiovascular phenotyping. Our screen recovered many genes encoding proteins in the cilia or centrosome, suggesting the cilium is a central disease pathway in CHD. To recover mutations causing CHD, we plan to use noninvasive fetal echocardiography to screen 100,000 mouse fetuses from 4000 pedigrees to achieve an estimated five-fold genome coverage (Aim 1). We will use a two-tier approach with high throughput targeted and whole genome DNA sequencing to identify the mutations (Aim 2). For genes suspected to have a role in the cilium, zebrafish will be used for rapid morpholino knock-down to analyze the motiie/nonmotile functions of the cilia and possible disruption of left-right patteming related to cilia defects (Aim 3). Mouse embryonic fibroblasts and tissues derived from mutant embryos will be used to evaluate cell-intrinsic function related to the cilium and centrosome (Aim 4). To elucidate the role of the cilia in cardiac morphogenesis, mutant embryos will be examined for heart looping, deployment of extracardiac cell populations to the heart, outflow tract and chamber septation. Cilia mediated sonic hedgehog and non-canonical Wnt signaling also ^ili be examined (Aim 5). In summary, the proposed studies will help elucidate the genetic basis for CHD. Many new CHD mouse models will be generated and the role of the cilium and other pathways playing important roles in CHD will emerge with the identification of a core set of genes critically involved in CHD. RELEVANCE (See instructions); The identification of a core set of genes involved in congenital heart disease can provide the basis for future translational studies with human subjects to elucidate the complex genetics of human congenital heart disease. This could include the design of diagnostic chips for genotyping patients with congenital heart disease and examining for correlation between genotype with disease phenotype and long term outcome.